Wavelength selectivity of a thermal IR-absorber as part of a fully integrated IR-absorption sensor

Previously we have shown that an appropriately designed waveguide can be used as an infrared absorption sensor element yielding comparable sensitivities to IR-transmission setups. We utilize the evanescent field of a monomode waveguide, which, together with a thermal IR-emitter and detector, will be integrated into a miniaturized sensor system. Besides the filter effect of the utilized grating couplers, a wavelength selective IR-detector is required to maintain the systempsilas functionality when using thermal non-polarized radiation. In this contribution, we consider the wavelength selectivity of the absorber structure of a thermal IR-detector. In contrast to previous investigations, we have expanded the assumption of a perfect back mirror towards a real metal of the non symmetric Fabry-Perot absorption structure. The presented analysis uncovers novel characteristics associated with this structure yielding the opportunity for a novel design requiring only one metal layer instead of two.